keep your cards close to your chest
keep (one's) cards close to (one's) chest
To keep one's plans, intentions, or information secret from everyone else. Refers to holding one's playing cards close to one's chest in a game, so as not to allow other players to see one's hand. We're all curious about what the boss has been discussing in those meetings with the lawyers, but she's been keeping her cards close to her chest. Sorry for not being more straightforward about my plans, but I'm keeping my cards close to my chest for the time being.
keep (or play) your cards close to your chest (or vest)be extremely secretive and cautious about something. informal
The previous two idioms both refer to a hand of cards in a card game. If you hold all the cards you have a winning hand, while card players who hold their cards close to their bodies ensure that no opponent can look at them.